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272

ALUMINIUM

(Al with 2-3% Mn) ; Duralumin (Al with 3'5^'5% Cu. 0-5-0-8% Mn,
o-5°/ Mg) " Zisium (Al with varying quantities of Cu, Sn, Zn) ; Alluman
(Al °vith 10-20% Sn, 4-6% Cu). There are also many other alloys of
aluminium, nickel and iron ; aluminium, copper, lead, nickel and iron, etc.

For commercial aluminium and its more important light alloys, a general
method of analysis will be indicated, whilst for light aluminium-bronze and
for magnalium, which could also be analysed by the general method, special
and quicker methods are given.

For aluminium-copper alloys in which the copper predominates (heavy
aluminium-bronzes, aluminium-brasses, etc.), reference should be made
to copper and its alloys and for iron-aluminium alloys (ferro-aluminiurn)
to ferro-metallic alloys.

The elements usually present as impurities in commercial aluminium
are copper, lead, iron, zinc, carbon, silicon and sodium. To form the so-
called light alloys, the aluminium may be associated with tin, copper, zinc,
nickel, cobalt, manganese, lead, magnesium, etc.

Thus, the analysis of commercial aluminium or of its lighter alloys
includes -1:

1. Determination of the Copper, Lead, Iron, Zinc, Manganese
and Cobalt.—A. IN ABSENCE OF NICKEL. From 2 to 4 grams of the sample
—according as the extraneous metals are present in larger or smaller pro-
portion—in minute fragments are treated in a flask (about |-litre) with
five times their weight of tartaric acid and a little water. The flask is
covered with a small funnel and a small quantity of hydrochloric acid
diluted with an equal volume of water added drop by drop. The action is
started by gentle heating and sometimes proceeds so vigorously as to require
cooling. When the evolution of hydrogen begins to slacken, a fresh quantity
of hydrochloric acid of the same concentration is added and the liquid
heated on the water-bath until the action is complete, care being taken to
use the least possible amount of acid. The heating is then continued for
some time, with addition of 2-3 c.c. of cone, nitric acid.

The solution, which is usually turbid owing to the presence of carbon
and silica, is treated with small quantities of 50% sodium hydroxide solution
until the voluminous aluminium hydroxide precipitate at first formed
redissolves in the excess of the reagent. Hydrogen sulphide is then passed
through until the supernatant liquid becomes faintly yellow and the solution
boiled for some minutes to facilitate separation of the sulphides, left for
a time on the water-bath and filtered into a 300 or 500 c.c. measuring flask,
the precipitate being washed with hot water containing a few drops of
sodium sulphide. The copper, lead, iron, zinc, manganese and cobalt
remain on the filter, while the aluminium passes into solution, together
with any tin present as sulphostannate.

The sulphides on the filter are dissolved in nitric acid (D 1-2) and the

1 Belasio : Annali di Chim. Appl., 1914, I, p. 101 ; Ann. Labor. Chim. Gabelle,
VII, p. 171.f Ordinary Brasses.